Method for controlling a storage roller and a storage roller for storing sheet-type objects

ABSTRACT

In a method for controlling a storage roller for storing sheet-type objects, in particular banknotes, between the wound layers of a belt-type film, which is spooled to and fro between a film drum, which is driven by a first motor and comprises a film reservoir roll, and a winding drum, which is driven by a second motor and stores the sheet-type objects, the tension of the film is controlled to a predefined set value.

[0001] The invention relates to a method for controlling a storage roller for storing sheet-type objects, in particular banknotes, between the wound layers of a belt-type film, which is spooled to and fro between a film drum, which is driven by a first motor and comprises a film reservoir roll, and a winding drum, which is driven by a second motor and stores the sheet-type objects.

[0002] Storage rollers are frequently used in automatic teller machines, since they permit the same banknotes to be stored and dispensed in a straightforward manner. In the case of filling or storing, the incoming banknotes are wound one after another onto the winding drum, between the wound layers. The rotational speed of the winding drum can in this case be adapted, for example on the basis of the counted banknotes. In the case of removing or dispensing the banknotes, these are unwound from the winding drum again on the “last in, first out” principle, the film running onto the film drum in the process.

[0003] In order that spooling the film to and fro does not lead to the film running out of a lateral guide that is present, the film must be kept continually under tension, in order to prevent the formation of a loop.

[0004] The most uniform tension possible in the film may be achieved, for example, by a friction brake acting in both directions. However, friction brakes have the disadvantage that they exhibit high changes in frictional torque, in particular after relatively long operating pauses or else as a result of temperature changes during relatively long operation. In order to compensate for this, that is to say always to ensure a reliable operating state, comparatively high frictional torques have to be set which, in turn, lead to corresponding wear on the entire mechanism, so that frequent maintenance and readjustment of the frictional torque is required. In addition, a correspondingly high power loss occurs.

[0005] The invention is based on the object of specifying a method of the type mentioned at the beginning in which, while avoiding the disadvantages mentioned previously, the formation of a loop of the film can reliably be avoided and power-saving operation of the storage roller can be ensured.

[0006] According to the invention, this object is achieved by the tension of the film being controlled to a predefined set value.

[0007] By controlling the film tension or film pulling force to a predefined low value, for example 10 newtons, a longer lifetime of the film can be guaranteed. Stretching processes, which are frequently observed and, in particular, occur at the edges of the plastic films and lead to cracks at the film edges or, because of the nonuniform extension of the film, to the film running out of its track, can be eliminated completely as a result. As a result of the fact that a low value for the film tension can be predefined and maintained, drive motors with lower powers can be used, which reduces the power consumption of the storage roller. The lower stressing of the film permits a reduction in the film thickness, so that, given the same overall space for the storage roller, the latter has a higher storage capacity.

[0008] For the control, the actual value of the film tension must be registered. This can be carried out by means of a direct measurement of the film tension, for example by the use of strain gages. The actual value of the film tension can, however, also be calculated indirectly from the determined power consumption of the first motor and the current radius and moment of inertia of the film drum.

[0009] Storage rollers, as has been explained above, are generally used in higher-order devices, for example cash handling devices, such as in automatic cash safes or in money recycling systems. This means that the storage roller must be able to store and dispense banknotes at a speed corresponding to the processing speed of the banknotes in the higher-order device. For this purpose, it is expedient if the circumferential speed of the winding drum can be controlled to a predefined set value. By controlling the circumferential speed, the storage and dispensing speed of the storage roller can be matched flexibly to changes in the higher-order system. In addition, by means of such control, the distances between the sheets or banknotes to be stored can be reduced to a minimum. This in turn leads to a higher storage capacity of the storage roller.

[0010] Given the simultaneous control of the circumferential speed of the winding drum and the film tension by means of driving the motors for the film drum and the winding drum, a system with multivariable control is obtained. The torques of both motors act both on the winding drum speed and on the film tension or pulling force of the film, in that, firstly, a predefined winding speed is to be reached, secondly, by means of appropriate driving of both motors, the drum discharging film is in each case braked slightly with respect to the drum accepting film, in order to tension the film between the drums. This means that the torque of the motor of the film drum also acts on the circumferential speed of the winding drum via the film tension which is actually to be influenced. Conversely, although primarily only the circumferential speed of the winding drum is to be controlled by the torque of the motor of the latter, a reaction on the film tension is also produced here. In order to be able to handle such multivariable control in practice, the physically coupled control loops for the film tension and the circumferential speed of the winding drum are decoupled by computation by means of a mathematical filter network, according to which the drive signals for the first and the second motor can be calculated on the basis of the determined actual values for the film tension and the circumferential speed of the winding drum, the rotational speed of the film drum and the predefined system parameters.

[0011] The invention relates further to a storage roller for carrying out the above-described method according to claims 8 to 16.

[0012] Further features and advantages of the invention emerge from the following description which explains the invention by using an exemplary embodiment in conjunction with the appended drawings, in which:

[0013]FIGS. 1-3 each show a schematic illustration of a storage roller to explain the mode of operation of the same,

[0014]FIG. 4 shows a schematic illustration of the important elements of the storage roller according to the invention and its connection to a control device,

[0015]FIG. 5 shows a simplified physical block diagram of the controlled system of the storage roller illustrated in FIG. 4 without the motors,

[0016]FIG. 6 shows a mathematical block diagram of the storage roller and

[0017]FIG. 7 shows a mathematical block diagram of the storage roller with decoupling filter.

[0018] The storage roller illustrated schematically in FIG. 1 comprises a housing 10 in which a film drum designated generally by 12 and a winding drum designated by 14 are mounted such that they can rotate about mutually parallel axes 16 and 18. The film drum 12 has a drum core 20, onto which a belt-type film 22 consisting of plastic can be wound up to form a roll 24, the minimum and the maximum diameters of the film roll 24 being indicated in FIG. 1. The film 22 runs from the film drum 12 over stationary deflection rollers 26 and a movable deflection roller 28 to the winding drum 14, where it runs onto a drum core 30 of the winding drum 14 and forms a storage roll 32. The movable deflection roller 28 is in this case held, by means not illustrated, in each case on the

[0019] circumference of the winding drum 14. The positions of the movable deflection roller 28 at minimum radius and maximum radius of the winding drum 14 are likewise indicated in FIG. 1.

[0020] In order to insert sheet-type objects, for example banknotes 34, into the gap between the circumferential surface of the winding drum 14 and the movable deflection roller 28, and thus between two wound layers of the film 22 running onto the winding drum 14, use is made of a slotted transport guide 36, which is adjustable, just like the movable deflection roller 28.

[0021] If the film drum 12 and the winding drum 14 are rotated in the counterclockwise direction according to FIG. 2, so that the film 22 runs onto the winding drum 14 in the direction indicated by the arrows in FIG. 2, banknotes 34 are wound into the roll 32, that is to say stored in the storage roller. If, on the other hand, the drums 12 and 14 are driven in the clockwise direction in the manner illustrated in FIG. 3, the film 22 runs from the winding drum 14 onto the film drum 12, the banknotes 34 being dispensed from the gap between the surface of the winding drum 14 and the movable deflection roller 28, that is to say being removed from store. The functioning described to this extent of a storage roller is known per se.

[0022]FIG. 4 shows the important elements of the storage roller and its linking with an open-loop and closed-loop control device. In this case, the elements coinciding with the illustration in FIGS. 1 to 3 are also provided with the same reference numbers.

[0023] The drum core 20 of the film drum 12 is connected to a shaft 38, which bears a toothed pulley 40. The latter is coupled by a toothed belt 42 to the drive pinion 44 of an electric motor 46.

[0024] In the same way, the drum core 30 of the winding drum 14 is connected to a shaft 48 which bears a toothed pulley 50. The latter is connected via a toothed belt 52 to the drive pinion 54 of a second electric motor 56.

[0025] Each of the electric motors 46 and 56 is coupled to an encoder 58 and 60, respectively, for example an incremental decoder, whose output signal is in each case supplied to a control device 62. The control device 62 receives a further input signal from a strain gage 64 which is used to measure the actual value of the film tension, it being possible for the current film tension also to be determined in another way, as was explained above.

[0026] On the basis of the rotational speed information determined by the encoders 58 and 60 and of the actual value of the film tension, the predefined set values for the film tension and the circumferential speed of the winding drum 14 and also the predefined system parameters, the control device 62 then determines drive signals for the motors 46 and 56 in order to drive the latter such that the predefined set values for the film tension and the circumferential speed of the winding drum 14 are maintained.

[0027] The block diagram according to FIG. 5 shows the coupling between the actuating variables and the controlled variables of the system. In this case, the formula symbols in FIG. 5 designate the following variables:

[0028] M_(G), M_(F)=torques of the motors 56, 46

[0029] V_(g), V_(f)=circumferential speeds of the drums 14, 12

[0030] F=film tension

[0031] d, c=damping and spring constants of the film

[0032] J_(G), J_(F)=moments of inertia of the drums 14, 12

[0033] r_(G), r_(F)=actual radii of the drums 14, 12

[0034] The controlled variables are the film tension F and the circumferential speed vg of the winding drum 14. The actuating variables are the motor torques M_(F) and M_(G). The torque M_(F) of the film drum motor 12 also acts on the speed V_(G) of the winding drum via the film tension F which is actually to be influenced. Primarily, only the circumferential speed V_(G) of the winding drum 14 is intended to be controlled by the torque M_(G) of the winding drum motor 56. However, a reaction on the film tension is also produced here, since the latter is certainly intended to be produced by means of a difference in the circumferential speeds of the film drum 12 and the winding drum 14.

[0035] The coupling between the actuating and controlled variables is reproduced by the mathematical block diagram according to FIG. 6. Here, Gi (s) designates the transfer functions which describe the dynamic behavior of the system. The arrows show the coupling paths between the actuating variables M_(F), M_(G) and the controlled variables F, v_(g).

[0036] In order to be able to handle such multivariable control in practice and to determine the required controllers, the coupling between M_(G) and F and, respectively, M_(F) and v_(g) must be eliminated. This can be done in a mathematical way by means of a filter network according to FIG. 7. This filter network comprises transfer functions V_(i) (s), which have to be determined such that the following system of equations is satisfied:

V ₁(s)·G ₃ (s)=V ₃(s)·G ₄(s)

V ₂(s)·G ₁(s)=V ₄(s)·G ₂(s)

[0037] If the above equations are satisfied, the undesired coupling paths in the system are eliminated by the filter network connected upstream, so that only the motor torque M_(G) is coupled to the circumferential speed v_(g) and the motor torque M_(F) is coupled to the film tension F. As a result, two control loops are produced which can be designed independently of each other.

[0038] During the design of the control, in addition to the above-described coupling of the system variables, it must be noted that, as a result of the film being wound and unwound, the radii of the drums and, associated with this, the moments of inertia of the same change. The radii and moments of inertia changing over time result in a nonlinear system behavior. The change in the radii can be described approximately by an Archimedean spiral: $r_{{film}\quad {drum}} = {r_{{drum}\quad {core}} + {\frac{a}{2\pi}\left( {\phi_{0} + \phi} \right)}}$

[0039] Explanation of the formula symbols:

[0040] r_(film drum)=actual radius of the drum with film

[0041] r_(drum core)=radius of the drum without film, that is to say radius of the drum core

[0042] a=thickness of the film

[0043] φ₀=starting angle of the drum

[0044] φ=actual angular position of the drum

[0045] The angular position φ of the drums can be determined by means of measurement and integration of the angular speed of the motors 46 and 56.

[0046] With the aid of the previously determined radii and the material characteristics of the film 22, the moment of inertia of the film is determined: $J_{film} = {\frac{1}{2}\rho_{film}b_{film}{\pi \left( {r_{{film}\quad {drum}}^{4} - r_{{drum}\quad {core}}^{4}} \right)}}$

[0047] Explanation of the formula symbols:

[0048] b_(film)=width of the film

[0049] P_(film)=density of the film

[0050] The respective film roll 24, 32 is in this case considered as a hollow cylinder which is plugged onto the respective drum core 20 or 30. The moments of inertia of the drum cores 20, 30 are constants and are determined from the constructional data.

[0051] In order to take account of the influence of the banknotes to be stored on the radius and the moment of inertia of the winding drum 14, a simple model was developed which describes the banknotes as a “paper layer” between the film layers. In the case of the paper layer, a density is calculated which takes into account the distances between the banknotes set by the control.

[0052] Since the rate of change of the radii and therefore of the moments of inertia at a required maximum winding drum speed v_(g) of 1.2 m/s is relatively low, the change over time of the system parameters can be compensated for by simple linear transfer functions with changing coefficients.

[0053] For the control of the film tension and the circumferential speed v_(g) of the winding drum 14, control concepts known from the literature, such as cascade control systems or else state control systems with observer, can be used. Irrespective of the respective direction of rotation, the motor 56 on the winding drum 14 then adjusts only the desired winding speed v_(g). The film drum motor 56, on the other hand, is responsible only for maintaining the desired film tension F.

[0054] Instead of an incremental encoder 58 on the film drum motor 46, a simple pulse transmitter or counter can also be used which, during each full revolution of the film drum 12, is incremented or decremented, since the moment of inertia of the film drum 12 changes only relatively little during each revolution and since the determination of the film drum speed is not absolutely necessary for the control of the entire system.

[0055] In order to measure the film tension, a strain gage 64 is used in the exemplary embodiment illustrated. However, the actual value of the film tension can also be determined indirectly by measuring the current in the motor 46 and by calculating the radius and the moment of inertia of the film drum 12. 

1. A method for controlling a storage roller for storing sheet-type objects, in particular banknotes, between the wound layers of a belt-type film (22), which is spooled to and fro between a film drum (12), which is driven by a first motor (46) and comprises a film reservoir roll (24), and a winding drum (14), which is driven by a second motor (56) and stores the sheet-type objects (34), characterized in that the tension of the film (22) is controlled to a predefined set value.
 2. The method as claimed in claim 1, characterized in that the actual value of the film tension is measured directly.
 3. The method as claimed in claim 1, characterized in that the actual value of the film tension is calculated from the determined power consumption of the first motor (46) and the current radius and moment of inertia of the film drum (12).
 4. The method as claimed in one of claims 1 to 3, characterized in that the circumferential speed (v_(g)) of the winding drum (14) is controlled to a predefined set value.
 5. The method as claimed in claim 4, characterized in that the rotational speed of the second motor (56) is measured by means of an encoder (60) and, from this, the actual value of the circumferential speed (v_(g)) of the winding drum (14) and its angular position is calculated.
 6. The method as claimed in one of claims 1 to 6, characterized in that the rotational speed of the film drum (12) is measured.
 7. The method as claimed in one of claims 4 to 6, characterized in that the physically coupled control loops for the film tension (F) and for the circumferential speed (v_(g)) of the winding drum (14) are decoupled by means of a mathematical filter network, and in that the drive signals for the first and the second motor (46, 56) are calculated on the basis of the determined actual values for the film tension (F) and the circumferential speed (v_(g)) of the winding drum (14), the rotational speed of the film drum (12) and the predefined system parameters.
 8. A storage roller for storing sheet-type objects, in particular banknotes (34), comprising a film drum (12) that can be driven by a first motor (46), with a reservoir roll (24) of a belt-type film (22), a winding drum (14) that can be driven by a second motor (56), it being possible for the film (22) to be spooled to and fro between the film drum (12) and the winding drum (14), means (36) for supplying sheet-type objects (34) between the wound layers of the film (22) as the same is wound up onto the winding drum (14) and for dispensing the sheet-type objects (34) as the film (22) is unwound from the winding drum (14), and a control device (62) for driving the first and second motor (46, 56), characterized in that the control device (62) is designed to control the tension of the film (22) between the two drums (12, 14) to a predefined set value.
 9. The storage roller as claimed in claim 8, characterized in that the control device (62) is designed to control the circumferential speed (v_(g)) of the winding drum (14) to a predefined set value.
 10. The storage roller as claimed in claim 8 or 9, characterized by a device (64) for measuring the actual value of the film tension (F).
 11. The storage roller as claimed in claim 10, characterized in that the device for measuring the actual value of the film tension (F) is a strain gage (64).
 12. The storage roller as claimed in claim 8 or 9, characterized by means for registering the power consumption of the first motor (46) and means (62) for calculating the actual value of the film tension (F) from the registered data and the current radius and moment of inertia of the film drum (12).
 13. The storage roller as claimed in one of claims 8 to 12, characterized in that an encoder (60) is assigned to the second motor (46).
 14. The storage roller as claimed in one of claims 8 to 13, characterized in that an encoder (58) is assigned to the first motor (56).
 15. The storage roller as claimed in one of claims 8 to 13, characterized in that a tachometer is assigned to the film drum (12).
 16. The storage roller as claimed in one of claims 9 to 15, characterized in that the control device (62) contains a program-controlled computer which is programmed in such a way that it calculates the function values of the resulting transfer functions, which correspond to the two control loops decoupled by a mathematical filter network, from the determined current and the predefined data and from this determines the drive signals for the first and the second motor (46, 56). 